EP2049960B1 - Method for the starting up of at least one field instrument - Google Patents

Abstract

Disclosed is a method for starting up of at least one first field instrument, wherein the method comprises the step of signaling a firs demand for electrical power output of the first field instrument over a first port to a supply unit. According to this method, the first field instrument is previously connected to the supply unit over the first port by means of a first communication connection. In addition, the reception of the power output is effected according to the first demand for power output by the first field instrument over the first communication connection and the first port, by which the first filed instrument is activated. In an additional step, a power usage unit of the first field instrument is assigned to the first port, wherein the power usage unit is provided as consumer load for the power output.

Description

The invention relates to a method for starting up and operating at least one field device in general and to a method for starting up a field device whose energy requirement is provided via an Ethernet connection (Power over Ethernet), in particular. In another aspect, the invention relates to a field device.

State of the art

Power over Ethernet (PoE) is a technology that provides power to network-enabled devices over the 8-wire Ethernet cable. In the narrower sense, PoE today is mostly the IEEE 802.3af standard, which was adopted in July 2003 in its final version. Previously, there were already some vendor-specific implementations that also traded under the name Power over Ethernet.

The key benefit of using Power over Ethernet is that you can save on a power cable and install Ethernet-attached devices in hard-to-reach places or in areas where many cables would interfere. Thus, on the one hand partly installation costs can be saved, on the other hand, the use of a central, uninterruptible power supply (UPS), which can be easily implemented, can increase the reliability of the connected devices.

Power over Ethernet is typically used by consumer devices that consume little power. examples for this are IP phones, small hubs, small cameras, small servers or wireless transmission devices (WLAN, ACCESS points, FSO devices, BlueTooth ACCESS points).

Power over Ethernet is also used in automation technology, for example in field devices in production or logistics applications. The individual field devices that make up a production or logistics application are networked via Ethernet technology.

According to the IEEE standard 802.3af, the participating devices are subdivided into power suppliers (Power Sourcing Equipment, PSE) and consumers (Powered Devices, PD). The energy providers are referred to below as supply units or as power supply units. Consumers are also referred to below as power take-off units. The supply voltage with which a consumer is supplied during operation is 48 volts. The maximum current consumption of the field devices is 350 mA in continuous operation. For a short time 400 mA are allowed when switching on. This results in a maximum power consumption of 15.4 watts. To transfer the power, both free wire pairs and the signal-carrying wires in the Ethernet cable are used.

The challenge for manufacturers of proprietary PoE solutions used to be to prevent damage to non-PoE-enabled devices.

The 802.3af standard solves this problem through a process called Resistive Power Discovery. In this case, the energy supplier, ie the supply unit, initially applies a minimal amount of current to the wires of the Ethernet connection via which a load is connected to the supply unit, whereby with the minimum current normally no device can be damaged. The energy provider recognizes whether and where the consumer has a 25 kohm connection resistance and is therefore capable of power over Ethernet. As a result, the consumer with a small Power and now has to signal to which of four defined in the standard performance classes it belongs. Only then the consumer gets the full power and can start operation.

The power supply of the field devices or the consumer can be done by so-called endspan devices (for example, switches) or midspan devices (units between switch and field device). As midspan devices mostly hubs are used, which supply power to the respective wires. For midspan infeed, a so-called power feeder or a midspan insertion panel is placed between the Ethernet switch and the field devices, ie the PD devices. These systems are similar to patch panels and typically have between 6 and 24 channels. Each power feeder has an input for the incoming data and a combined output for data and power via PoE.

The total supply power provided by such an Ethernet switch or power feeder is limited for power loss reasons. Each terminal can request a specific performance budget at its line connection, ie at its port, via which the field device is connected to the supply unit. This power budget is classified in several stages by the field devices via a defined power impedance as mentioned above.

In many industrial applications, Ethernet technologies with a line structure are used. Such line structures are advantageous, for example, in manufacturing or logistics applications. The field devices that communicate with each other in a line structure must each have at least two communication ports. One of these ports is used, for example, to connect to the higher-level system or a switch. A second port is used to forward the data to the neighboring field device.

In such constructed line or ring topologies, the power supply according to the standardized Power over Ethernet method according to the IEEE standard 802.3af can not be applied to a plurality of, for example, in line PoE field devices. One reason is that the feeding PSE switch or feeding power feeder can not supply power to multiple consumers in series because only the consumer immediately adjacent to the Power over Ethernet switch or power feeder can signal its own power requirements. The first in line consumer could always request the maximum power budget. On the one hand, this would not be compliant with IEEE 802.3af, since its actual power consumption is usually much lower. On the other hand, this maximum power budget can be exceeded by downstream consumers, which will lead to the shutdown of the entire line by the supply unit.

From the WO 2006/032588 A1 For example, a communication system according to the IEEE standard 802.3af is known in which modular network devices are used. A modular network device consists of several network elements arranged one behind the other in a line. Each of the network elements has an electrical resistance as a passive component. These are interconnected in the interconnection of the network elements via a bus. The first network element of the network device determined by means of an assembly the resulting total resistance on the bus as a characterizing parameter that allows a statement about the power requirements of the modular network device. In this way, the actual energy requirement of the network device can be signaled to a supply device.

From the EP 0 836 966 A2 an arrangement for electrical power supply is known in which consumers are arranged along a power supply line in a ring. By a test device, a short circuit fault in the Supply line can be determined. If there is an error, a switch device prevents the supply voltage from being switched through to a short circuit.

The object of the invention is therefore to provide an improved method for starting up at least one field device, so that according to the method also a plurality of field devices connected in series, e.g. in a line structure or ring structure. The object of the invention is also to provide an improved field device.

The objects underlying the invention are each achieved with the features of the independent claims. Embodiments of the invention are indicated in the dependent claims.

The invention provides an improved method for starting up at least one first field device, the method comprising the step of signaling a first electrical power requirement of the first field device via a first port to a supply unit, wherein the field device has been previously connected to the supply unit via the first port by means of a first communication connection. The method further comprises the step of receiving the electrical power corresponding to the first electrical power demand by the first field device via the first communication link and the first port, thereby activating the first field device. Further, the method comprises the step of assigning a power extraction unit of the first field device to the first port, wherein the power extraction unit is provided as a consumer for the power. In addition, the method comprises the step of assigning a power supply unit of the first field device to a second port, wherein the power supply unit is provided for the provision of a second power requirement via the second port.

After connecting the first port via the first communication connection to the supply unit, the first field device signals its first power requirement. Signaling here means, for example, that on the side of the field device, an impedance of defined size (25 kOhm) is present as a device-specific signature, so that the field device as provided by the IEEE standard 802.3af can be recognized as a PD device of the supply unit and thereby the first electrical power requirement of the first field device can be determined by the supply unit. The supply unit can then activate the field device by providing the power corresponding to the first power requirement, which is picked up by the field device. The field device has a power extraction unit, which is then assigned to the first port. The power extraction unit is provided as a consumer for the provided power. The field device thus has PD characteristics at the first port. Furthermore, the power supply unit of the field device is assigned to the second port. The first field device thus has PSE properties on the second port.

According to one embodiment of the invention, the method further comprises the step of detecting a second field device via the second port of the first field device, wherein the second field device has previously been connected to the second port of the first field device via a second communication link. Furthermore, the second electrical power requirement of the second field device is determined via the second communication connection. In a further step, the determination of the total electrical power requirement from the first and second electrical power requirements. Furthermore, the transmission of the entire electrical power requirement to the supply unit takes place. In a further method step according to the invention, the total power is absorbed by the first field device in accordance with the total power requirement, the entire power being provided by the supply unit if the supply unit can provide all the power. In addition, the second field device is supplied with the power corresponding to the second electrical power requirement in the event that the entire power is obtained by the first field device.

Thus, after the first field device has been put into operation by the supply unit, the second field device is connected to the supply unit via the first field device and via the first and second communication links and put into operation by the first field device. The invention is particularly advantageous because a plurality of consumers connected in series can be supplied with power from an upstream supply unit. As already mentioned above, this is not provided in the IEEE standard 802.3af.

According to a further embodiment of the invention, the method further comprises the step of monitoring the second port fed by the first field device. The inventive method further comprises the step of interrupting the supply of the second field device in the event of a short circuit or an overcurrent in the second communication link. A self-organization of the PoE line results from the fact that each field device, as here the first field device during operation, continuously monitors the outgoing port it feeds, such as the second port, for example. In the case of overcurrent or short-circuit in the outgoing connection, the feeding device interrupts the power supply to the neighboring device, as here to the second field device. Thus, a selectivity is given in case of error, ie it is not the entire line, but only the devices affected by the short circuit are disconnected from the power supply.

According to an embodiment of the invention, the method according to the invention further comprises the step of storing a portion of the received electrical energy and the step of monitoring the feeding first port. As a result, an interruption of the power supply of the first field device can be detected. Further, the step of interchanging the assignment of the power extraction unit and the power supply unit to the first and second ports follows if an interruption of the power supply is detected.

By monitoring the feeding port, an interruption of the power supply can be detected in good time. The field device, as here for example the first field device, can then swap the assignment PSE / PD to its ports. If the field device is installed, for example, in a ring topology, then, with suitable buffering or energy storage of a part of the electrical energy already received by the field device, the device can remain active despite the interruption of the current and reverse the energy flow direction, for example, feeding it from the second port becomes.

According to one embodiment of the invention, a change in the second power requirement of the second field device is detected by the first field device, wherein the changed total power requirement is transmitted to the supply unit and wherein the power corresponding to the changed second power requirement is made available to the second field device in the event that the power is received by the first field device according to the changed total power requirement. The first field device can thus detect a change in the second power requirement of the second field device at any time during operation and accordingly request a changed total power requirement from the supply unit. This is advantageous, for example, if a third device is connected to the second device, which then, like the second field device, has been put into operation by the first field device, is now put into operation by the second field device. The second field device then reports, as a changed second power requirement, the power requirement of itself and of the third field device to the first field device, which accordingly transmits the changed total power requirement to the supply unit. In the event that the first device can absorb the changed total power requirement, it provides the second field device with the corresponding requested power. The second field device can then activate the third field device as described above for the first and second field device. The method according to the invention has the advantage that linear structures or even ring structures can now be realized by the configuration of the field devices according to the invention. The field devices adjacent to the feeding switch or power feeder are activated one after the other. This process does not result in a noticeable delay in communication during commissioning. Furthermore, the method according to the invention requires no special configuration of the individual field devices. Another advantage is that the power budget available for the line structure or for the ring structure and the power consumption of the connected devices are aligned with each other activated device, since the device preceding the other device always request the required power from the previous device got to. An overload of the entire line structure is thereby excluded.

According to one embodiment of the invention, the entire power requirement or the changed total power requirement is transmitted from the field device to the supply unit by means of the SNMP protocol (Simple Network Management Protocol).

According to one embodiment of the invention, the second field device is detected by the first field device by means of the LLDP protocol (Link Layer Discovery Protocol).

According to one embodiment of the invention, the field devices in the de-energized state on the first and second ports to a device-specific signature, the device-specific signature identifies the field devices as power extraction units, the device-specific signature is deactivated after activation of the field device. As already mentioned above, the devices according to the invention in the de-energized state at their ports on a signature with which they are recognizable as PD devices according to the IEEE 802.3af standard. In particular, since the second port, which is used as a PSE port when the field device is activated, must no longer have any PD functionality for the activated device, the device-specific signature is deactivated after activation of the device.

According to one embodiment of the invention (the second power requirement of the second field device is determined via the device-specific signature of the second field device.

According to one embodiment of the invention, the actual power consumption of the connected devices can be transmitted after activation of the devices via the SNMP protocol. By summing the individual exact powers, this power specification leads to an overall lower total power, which must be provided as a power budget by the supply unit. In contrast, the summation of the only three possible power levels of 4W, 7W, and 15.4W, as defined in classic PoE, always results in an unnecessarily high power budget.

According to one embodiment of the invention, the device-specific signature is realized by means of a power termination impedance according to the IEEE 802.3af standard.

According to a further embodiment of the invention, the first communication connection and the second communication connection are based on the Ethernet technology.

According to one embodiment of the invention, the supply unit is a field device connected upstream of the first field device or a Power over Ethernet switch or a power feeder.

In another aspect, the invention relates to a field device having at least a first and a second port, with at least one power supply unit, wherein the power supply unit can be assigned to the first port and wherein the power supply unit is provided for the provision of electrical power via the assigned port. The field device furthermore has at least one power extraction unit, wherein the power extraction unit can be assigned to the at least second port, wherein the power extraction unit is provided as a consumer for the electrical power received via the assigned port.

FIG 1

zeigt ein Blockdiagramm einer Linienstruktur mit einer Versorgungseinheit und einem ersten und zweiten Feldgerät,

FIG 2

stellt in einem Flussdiagramm wesentliche Schritte des erfindungsgemäßen Verfahrens dar,

FIG 3

zeigt ein Ablaufdiagramm, das die Abläufe zwischen der Versorgungseinheit und dem ersten und zweiten Feldgerät bei Inbetriebnahme der Feldgeräte zeigt,

FIG 4

zeigt schematisch die Struktur eines Netzwerks, das Linienstrukturen und eine Ringstruktur aufweist,

FIG 5

zeigt ein Blockdiagramm eines Feldgeräts,

FIG 6

stellt schematisch in einem Blockdiagramm eines Feldgeräts die Potentialtrennung zwischen beiden Ports des Feldgeräts dar,

FIG 7

zeigt ein Blockdiagramm eines Feldgeräts mit T-Stück-Funktionalität,

Embodiments of the invention are explained below with reference to the drawings.

FIG. 1

shows a block diagram of a line structure with a supply unit and a first and second field device,

FIG. 2

illustrates in a flowchart essential steps of the method according to the invention,

FIG. 3

shows a flowchart showing the processes between the supply unit and the first and second field device when commissioning the field devices,

FIG. 4

schematically shows the structure of a network having line structures and a ring structure,

FIG. 5

shows a block diagram of a field device,

FIG. 6

schematically shows in a block diagram of a field device, the potential separation between the two ports of the field device,

FIG. 7

shows a block diagram of a field device with T-piece functionality,

FIG. 1 1 shows a block diagram of a line structure 100. In this case, the line structure 100 has a supply unit 102, a first field device 104 and a second field device 106. The supply unit 102 is a device that has PSE functionality according to the IEEE standard 802.3af. The Supply unit 102 is externally supplied with electrical energy. The supply unit 102 also has a processor 108, a memory 110 and ports 112, 114, 116 and 118.

The first field device 104 has a first port 120 and a second port 122. The first field device 104 additionally has a power extraction unit 124 and a power supply unit 126. Furthermore, the first field device 104 has a processor 130 and a memory 132.

The second field device 106, like the first field device 104, has a first port 134, a second port 136, a power extraction unit 138, a power supply unit 140 and a processor 142.

The power extraction units 124 and 138 have the functionality of a PD device according to the IEEE standard 802.3af. The power supply units 126 and 140 have the functionality of a PSE device according to the above standard. Thus, the first field device 104 and the second field device 106 have both PD and PSE functionality.

The first field device 104 signals at its ports 120 and 122 in the de-energized state PD properties according to IEEE standard 802.3af. For this purpose, the power extraction unit 122 is connected in the de-energized state to the first port (indicated by the solid line between the power extraction unit 124 and the first port 120) and to the second port 122 (dashed line between power extraction unit 124 and second port 122). Thus, the field device 104, when it is connected via a first communication link 144, for example via the port 120 and the port 112 to the supply unit 102, the supply unit 102 signals its PD properties.

The supply unit 102 can thus determine the first electrical power requirement 146 of the first field device 104 in accordance with the above-mentioned standard and provide the power corresponding to the first power requirement 146 to the first field device 104. By absorbing the power, the first field device 104 is activated.

The first port 120 is now assigned the power extraction unit 124. The PD signaling on the second port 122 is disabled. The power supply unit 126 is assigned to the second port 122. Thus, the second port has 122 PSE properties.

Activation of the first field device 104 also activates the processor 130. The processor 130 executes a computer program product 148 which is loaded at start-up of the processor 130 from the memory 132 on which the computer program product 148 is permanently stored.

The second field device 106 signals in the de-energized state at its ports 134, 136 its property as PD device, as previously the first field device 104. Now, the second field device 106 via its first port 134 and a second communication link 150 to the second port 122 connected, the first field device 104 may detect the second field device 106. For this purpose, the computer program product 148 uses, for example, the LLDP protocol (Link Layer Discovery Protocol).

The power supply unit 126 can then determine the second electrical power requirement 152 of the second field device 106 in accordance with the IEEE 802.3af standard. The computer program product 148 then determines from the first power requirement 146 and the second power requirement 152 a total electrical power requirement 154, the total power requirement 154 corresponding to the sum of the first power requirement 146 and the second power requirement 152.

The computer program product 148 now sends a first message via the communication link 144 to the supply unit 102, for example by means of SNMP (Simple Network Management Protocol), the entire power requirement 154 being transmitted to the supply unit 102 with the message.

The processor 108 executes a computer program product 156 that is permanently stored on the memory 110 and is loaded into the processor 108 at the start of the supply unit 102. By means of the computer program product 156, the total power requirement 154 is read from the received message and it is checked whether the supply unit 102 can make available the entire electrical power requirement 154. If so, the computer program product 156 sends a second message to the first field device 104 confirming the replenishment of the power provided.

As soon as the entire power requirement 154 is received by the first field device 104, the first field device 104 provides the second field device 106 with the power corresponding to the second power requirement 152. The second field device 106 is thus activated. The power extraction unit 138 is then assigned to the first port 134 so that the second field device 106 has PD functionality at this port. Further, the second port 136 is then assigned the power supply unit 140 so that the second port 136 has PSE functionality.

At the second port 136, another field device (in FIG. 1 not shown). The further field device is then put into operation by the second field device 106 in the same way as this second field device 106 has previously been put into operation by the first field device 104. In this case, the second field device 106 determines the total power requirement via the processor 142 and the corresponding computer program product (such as computer program product 148) the second field device and the other field device. The second power requirement 152, which is now transmitted to the first field device, corresponds to the total power requirement of the second field device 106 and the further field device.

All field devices, including the field device 104, continuously monitor the supplied ports. Thus, the first field device 104 can then detect the new total second power requirement. This changed second power requirement now affects the total power requirement 154, which also changes. The changed total power requirement is now reported to the supply unit 102, as previously the total power requirement 154. If the supply unit 102 can make the changed total power requirement available, the first field device 104 can absorb this total power requirement and thus make the power corresponding to the changed second power requirement available to the second field device 106. The second field device 106 can then activate the further device by providing the corresponding power. Thus, a line structure can be constructed, which is fed by an upstream supply unit 102.

FIG. 2 shows in a flowchart process steps of a method for starting up at least a first field device. In step 200, the signaling of a first electrical power requirement of the first field device via a first port to a supply unit, wherein the field device has been previously connected via the first port by means of a first communication connection to the supply unit. In step 202, the power corresponding to the first electrical power requirement is absorbed by the first field device via the first communication connection and the first port, whereby the first field device is activated. In step 204, a power extraction unit of the first field device is assigned to the first port, wherein the power extraction unit is provided as a load for the power. Further, in step 206 the allocation of a power supply unit of the first field device to a second port, wherein the power supply unit is provided for the provision of a second power requirement.

FIG. 3 shows a flowchart 300, which shows the processes between the supply unit 102, the first field device 104 and the second field device 106 when commissioning the field devices 104 and 106. In this case, the corresponding reference numerals for identifying the supply unit and the field devices or their ports were made FIG. 1 accepted. The first field device 104 has the first port 120 and the second port 122. The second field device has the first port 134 (the second port is not shown here for convenience).

The dashed lines below the supply unit 102, the first port 120, the second port 122 and the first port 134 relate to the time sequence of the processes in the corresponding units. The processes between the respective units are indicated by the horizontal solid arrows. Above the arrows there is a number to indicate the expiring step. After the corresponding number follows a short description of the step. The arrows also represent PoE connections between the supply unit 102 and the first port 120 and between the second port 122 and the first port 134, respectively. The arrow direction of the dashed vertical lines also indicates the direction of time.

In step 302, the first electrical power requirement (LB) of the first field device 104 is detected by the supply unit 102. In step 304, the power corresponding to the first electrical power requirement is provided via the first port 120 for the field device 104 active in step 306. In step 308, the power extraction unit (LEE) is assigned to the first port, and in step 310, a Assignment of the power supply unit (LVE) to the second port 122.

In step 312, the second field device (FG) 106 is detected by the first field device 104 via the second port 122. In step 314, the second electrical power requirement (LB) of the second field device is also detected. Furthermore, in step 316, the transmission of the first message, which contains information about the total electrical power requirement, which is composed of the first power requirement and the second power requirement, is transmitted to the supply unit 102.

In the event that the supply unit 102 can provide the requested total power requirement, the entire power requirement for the first field device 104 is provided in step 318. The supply unit 102 transmits the second message to the first field device 104 in the following step 320 the provision of the total power requirement is announced or otherwise denied. The first field device 104 optionally makes the second power requirement available to the second field device 106 in step 322. Thus, the field device, as previously in FIG. 1 described, activate.

FIG. 4 12 schematically illustrates the structure of a network 400 having line structures 402, 404 and a ring structure 406. The line structures 402 and 404 and the ring structure 406 in this case have a Power over Ethernet switch 408 as a common node. The power over Ethernet switch 408 has the functionality of the supply unit according to the invention.

The individual black-filled circles in the line structures 402 and 404 and in the ring structure 406 represent field devices 410 that have been put into operation according to the method described above. The energy required for operation is provided by the Power over Ethernet Switch 408 for all field devices, such as for the field device 410, in the line structure 402, in the line structure 404 and in the ring structure 406 provided.

The use of the ring structure 406 has the advantage that a redundant energy supply of the field devices according to the invention can thus be achieved. For example, the field devices along the path 412 may have been activated in the direction of the arrow of the path 412, respectively. Then field device 418 is powered by field device 416 and field device 418 powers field device 422. Similarly, the field devices along path 414 may have been activated in accordance with the arrow direction of path 414. Then field device 410 is the feeding device of field device 420.

If, for example, the field device 410 fails or the line between the field device 410 and the field device 420 breaks, the field device 420 can detect the interruption of the energy supply in good time due to the continuous monitoring of the feeding port described above. With suitable energy storage in the field device 420, the field device can now swap the assignment PSE / PD at its ports and can thus exchange the energy flow direction without interrupting the device function. The field device 420 may then receive power via the field device 422, and then the device 422 reports the changed power budget to the device 418, which in turn reports the changed power budget to the device 416, and so on.

If the field device 420 has no energy store, it is temporarily deactivated and then reports its PD signature to the field device 422. The field device 422 can then commission the field device 420 in accordance with the method.

FIG. 5 shows a block diagram of a field device 500. The field device 500 in this case has a first port 502 and a second port 504. The field device 500 further has two power extraction units 506 and 508 and two power supply units 510 and 512 on. The field device 510 further has a control logic 514 and diodes 516. The control logic 514 acts on all function blocks 506, 508, 510, and 512. Each port 502, 504 is associated with both a power extraction unit and a power supply unit. The first port 502 is associated with the power extraction unit 506 and the power supply unit 510. The second port 504 is associated with the power extraction unit 508 and the power supply unit 512. For the forwarding of the recorded electrical power via the first port 502 or via the second port 504, the power extraction units 506 and 508 and the power supply units 510 and 512 are cross-coupled. The device's own power supply is combined from both power draw units 506 and 508 via diodes 516 and via the device's own power supply 518 (PoE in).

When de-energized, the power draw units 506 and 508 provide a standard PD signature on the associated ports 502 and 504.

After activation of the field device 500 by an upstream supply unit, the PD signature on the non-powered ports is deactivated and the power extraction unit is assigned to the powered port. In addition, the power supply unit is assigned to the non-powered port. If e.g. supplies the field device 500 via the port 502, the power extraction unit 506 is assigned to the port 502; the power supply unit 510 is disconnected from the port 502. Accordingly, the power supply unit 512 is then assigned to the port 504 and the power extraction unit 508 is disconnected from the port 504.

For the forwarding of the recorded electrical power via the first or the second port 502 or 504, the power extraction units 506 and 508 or the power supply units 510 and 512 are cross-coupled (the arrow directions indicate the energy flow). The PoE power supply The device is combined from both power extraction units 506 and 508 via diodes 516 or other suitable coupling and used for the self-power supply 518 of the device (PoE In). During operation, the power extraction units as well as the power supply units 506 to 512 may have extended functionality. For example, in the case of a projectable power budget, the power class of the power draw units 506 and 508 may be switched by means of the control logic 514.

According to a further embodiment, a field device has only one power extraction unit and one power supply unit. The corresponding units are assigned to the corresponding ports after activation of the field device. This in FIG. 5 shown field device thus has a redundancy, since two units are shown.

FIG. 6 schematically illustrates in a block diagram of a field device 600, a potential separation between two ports 602 and 604 of the field device 600. The field device has, as previously in FIG. 5 described field device, two power supply units 610 and 612 and two power extraction units 606 and 608 on. The device further includes DC / DC converter 614 (DC / DC converter) and a self-supply (PoE in) 616. The power extraction unit 606 and the power supply unit 610 are assigned to the first port 602. The power extraction unit 608 and the power supply unit 612 are assigned to the second port 604. The self-power supply of the field device 600 takes place from both power extraction units 606 and 608 via the DC / DC converters 614 in the intrinsic supply 616 (PoE In) of the device 600. By using the DC / DC converters 614, the first and the second ports can be used Decouple 602 or 604 galvanically.

FIG. 7 shows a block diagram of a field device 700 with Tee functionality. The T-piece functionality is often required in industrial environments for line and ring topologies. With regard to the power / voltage supply of the line PoE devices, this means that the field device 700 has a communication unit 702 and further device components 704, the communication unit 702 being supplied with electrical energy both via the communication ports via PoE and via an independent device power supply can. The other device components 704 are supplied externally via a voltage input 710 with electrical energy. In the event of a failure of the device power supply, the communication unit can continue to be powered by PoE via ports 706 and 708 according to the invention with electrical energy, whereby a forwarding of the data is ensured via the communication unit.

According to a further embodiment, the field device may have a PoE-independent self-power supply, which not only supplies the communication unit 702 with energy, but also enables a transmission of this energy via the power supply units to adjacent field devices. With this embodiment, additional entry points for PoE can be created within a line.

Claims (21)

1. Method for starting up at least one first field device (104), wherein the method comprises the following steps of:

   - signalling a first electrical power requirement (146) of the first field device via a first port (120) to a supplying unit (102), with the first field device previously having been connected to the supplying unit via the first port by means of a first communication link (144);

   - drawing the power according to the first power requirement by the first field device via the first communication link and the first port, with the first field device being activated as a result; and

   wherein the method is characterised by the further steps of:

   - allocating a power drawing unit (124) of the first field device, which power drawing unit can be allocated to the first port or to a second port (122), to the first port, with the power drawing unit being provided as a consumer load for the drawn power; and

   - allocating a power supplying unit (126) of the first field device, which power supplying unit can be allocated to the first port or to a second port (122), to the second port (122), with the power supplying unit being provided for the purpose of delivering a second power requirement (152) via the second port.
2. Method according to claim 1, further comprising the steps of:

   - detecting a second field device (106) via the second port (122) of the first field device (104), with the second field device previously having been connected to the second port (122) of the first field device via a second communication link (150);

   - determining the second power requirement (152) of the second field device via the second communication link;

   - determining the total power requirement (154) from the first and second power requirements;

   - transmitting the total power requirement to the supplying unit;

   - drawing all of the power according to the total power requirement provided the supplying unit (102) can deliver all of the required power; and

   - supplying the second field device with the power according to the second power requirement (152) provided all of the power is received.
3. Method according to claim 2, further comprising the steps of:

   - monitoring the second port (122) fed by the first field device (104); and

   - interrupting the supply to the second field device (106) in the event of a short-circuit or excess current in the second communication link (150).
4. Method according to claim 2 or 3, further comprising the steps of:

   - storing a portion of the electrical energy received;

   - monitoring the feeding first port (120), thereby enabling an interruption of the energy supply to the first field device to be detected; and

   - transposing the assignment of the power drawing unit and the power supplying unit to the first and second ports if an interruption of the energy supply is detected.
5. Method according to one of claims 2 to 4, wherein a change in the second power requirement (152) of the second field device (106) is detectable by the first field device (104), with the changed total power requirement being transmitted to the supplying unit and with the power being made available to the second field device according to the changed second power requirement provided the power can be drawn by the first field device according to the changed total power requirement.
6. Method according to claim 5, wherein the total power requirement (154) or the changed total power requirement is transmitted to the supplying unit by means of the SNMP (Simple Network Management Protocol) protocol.
7. Method according to claim 2, wherein the second field device (106) is detected by the first field device (104) by means of the LLDP (Link Layer Discovery Protocol) protocol.
8. Method according to one of claims 2 to 7, wherein in the powerless state the field devices (104, 106) have a device-specific signature at the first and second ports, with the device-specific signature identifying the field devices as power drawing units, with the device-specific signature of the port not being fed being deactivated after reception of the power requirement.
9. Method according to claim 8, wherein the second power requirement (152) of the second field device (106) is determined via the device-specific signature of the second field device.
10. Method according to claim 8 or 9, wherein the device-specific signature is implemented by means of a power termination impedance in accordance with the IEEE 802.3af standard.
11. Method according to one of the preceding claims, wherein the communication links are based on Ethernet technology.
12. Method according to one of the preceding claims, wherein the supplying unit (102) is a field device connected upstream of the first field device (104) or a Power over Ethernet switch or a power feeder.
13. Field device (104) comprising:

    - at least one first (120) and one second port (122);

    - means for signalling its power requirement (146) to the first port (120);

    - at least one power drawing unit (124),
    characterised in that

    - the field device (104) has at least one power supplying unit (126), with the power supplying unit being allocatable to the first port (120), with the power supplying unit being provided for the purpose of delivering electrical power via the allocated port,

    - the power drawing unit (124) can be allocated to the at least one second port (122), with the power drawing unit being provided as a consumer load for power received via the allocated port,

    - means for signalling the power requirement (146) of the field device (104) are present at the second port (122), and

    - after the power requirement has been delivered by a supplying unit (102) via the first port (120) the power drawing unit (124) can be allocated to the first port (120) and the power supplying unit (126) can be allocated to the at least one second port (122).
14. Field device (104) according to claim 13, further comprising:

    - means for detecting a second field device (106), with the second field device (106) previously having been connected to the second port (122) of the field device (104);

    - means for determining a second power requirement (152) of the second field device;

    - means for determining a total power requirement (154), with the total power requirement including the power requirement of the first field device and the second power requirement;

    - means for transmitting the total power requirement to the supplying unit (102), with the field device previously having been connected to the supplying unit; and

    - means for delivering the second power requirement for the second field device (106).
15. Field device according to claim 14, further comprising:

    - means for monitoring device the second port (122) fed by the first field device (104); and

    - means for interrupting the supply to the second field device (106) in the event of a short-circuit or excess current in the second communication link (150).
16. Field device according to claim 14 or 15, further comprising:

    - means for storing a portion of the electrical energy received;

    - means for monitoring the feeding first port, thereby enabling an interruption of the energy supply to the first field device to be detected; and

    - means for transposing the assignment of the power drawing unit and the power supplying unit to the first and/or second port if an interruption of the energy supply is detected.
17. Field device according to one of claims 14 to 16, further comprising:

    - means for detecting a change in the second power requirement of the second field device; and

    - means for requesting the corresponding changed total power requirement from the upstream supplying unit.
18. Field device according to one of the preceding claims 13 to 17, further comprising control logic (514), wherein the allocation of the power supplying unit (510, 512) and the power drawing unit (506, 508) is controlled by the control logic.
19. Field device according to claim 18, wherein the power supplying unit (510, 512) and/or the power drawing unit (506, 508) have a plurality of operating modes, with the operating modes being settable via the control logic (514).
20. Field device according to one of the preceding claims 13 to 19, wherein the at least one power supplying unit (610, 612) and the at least one power drawing unit (606, 608) are potentially isolated from one another.
21. Field device according to one of claims 14 to 20, further comprising means for storing the first power requirement, the second power requirement and the total power requirement.

Images